Hi all,

I just purchased a 2000 f-250 5.4l, it had a cyliner #8 misfire code when i bought it a few days ago. Im going through right now changing out the plugs, so far i have 5-8 done. #5 plug & boot were covered in oil, 6 & 7 had a little oil in the spark plug well, but #8 was the worst of all it has a lighter brown almost like clay or mud all over the plug and boot. See pics in the link

There doesnt appear to be any oil leaking from the valve cover, what are the most likely culprits? As well as any ideas on what the brown gunk is, is this most likely a head gasket?

Thanks all,
Drew

Boot
https://photos.app.goo.gl/Um77LNHVY4QDAZ263

SP Well
https://photos.app.goo.gl/4LFmZ9RwbojxEc2r1

Brown Gunk
https://photos.app.goo.gl/QPsjiSAh02lugWFc2

 

A more info, I bought the truck from a company, it was used as a work truck so i really dont have any maintenance history on it. I bought it about a month and ive maybe put 100 miles on, all in all its driven well its just a had hesitation like a dead cyliner. I plugged my scanner in to read live data, at idle timing @ #1 was right around 8deg advanced for 10sec then it would shoot up to 30 deg advanced for about 3 seconds and repeated that cycle.

 

Bump this post

 

Most likely the intake gasket, 5.4s are known for bad intake gaskets.

 

When I bought my truck it had just had its 3rd intake gasket done. I'm pretty sure their mechanic was doing something wrong. Either way I got a great price on it because of the issues. Over the summer I believe it was #2 cylinder by the tstat housing filled up with coolant, making it misfire. I'm thinking it may have been bad all along and their mechanic missed it. I was smelling coolant for over a year every time I'd pop the hood everything was dry as a bone. I just sucked the hole out, threw a new coil, boot and wire in alls been well. I finally caught a drip on the tstat housing the other week. So that will be my next project.

Don't sound like your issue though #8s on the passenger rear right? I had a little bit of oil back there on the intake when I did the plugs a few years ago but non in the hole. Intakes probably bad too but I'll probably just keep driving it until it completely fails.

 

.I have 2001 5.4 engine couple of years ago it developed intermittent misfire. it was the intake leaking. usually was ok cold and once it warmed up started missing. coolant leaks, shorts the plug then it evaporates and cycle repeats. you might get away with gaskets but no guarantee. in my case I replaced intake from a company called Dorman. Have had no issues. One last point good investment replacing thermostat every 2 years. If it sticks the pressure will make the gaskets leak. allways keep an eye on temperatuire gauge